240SCIENCE
Light fantastic
Energy takes many forms. Light is one we are familiar with
because our eyes are specially adapted to detect it. However
seeing light is one thing – understanding it is more tricky.
Where does light come from?
Atoms that are excited by a collision return to
their normal state by emitting light energy. The
atoms in a heated lightbulb filament shed their
excess energy by flinging out tiny packets of light
called photons, causing the filament to glow.OLight is the fastest moving thing in the Universe. It travels across empty space at the
unimaginable speed of 300,000 km/second (186,411 miles/second).
OOne light year is the distance light can travel in one year. This is about 9.5 trillion km
(5.9 trillion miles). Light years are used to measure colossal distances across space.
The Sun is a mere 499 light seconds away.
OAlbert Einstein worked out that if there was a way to travel at close to light speed,
time would slow down and you would age more slowly.Shadows
Light travels in a straight line, and
cannot bend round obstacles. The space
behind an obstacle looks dark because
the only light reaching it is that reflected
from other objects nearby.THE SPEED OF LIGHT
HOW DOES LIGHT TRAVEL?
Puzzlingly, light behaves as though it is
made of both waves and particles. Like
waves, light can be reflected and refracted,
and its wavelength can be measured. Other
types of wave need something (a “medium”),
to ripple through, but light can travel
across a vacuum.IL
GHTWAVESLI
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ALL A BLUR
Fast-moving objects
appear blurred because
light travels much
faster than our brain
takes to interpret what
we are seeing.
Filament
(c) 2012 Dorling Kindersley. All Rights Reserved.(c) 2012 Dorling Kindersley. All Rights Reserved.